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scrollTo.js
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scrollTo.js
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import safeScrollTop from './safeScrollTop';
// For a best approach to fix the header height
// https://css-tricks.com/hash-tag-links-padding/
/**
* t = current time
* b = start value
* c = change in value
* d = speed
*/
const easeInOutQuad = (t, b, c, d) => {
let currentTime = t / (d / 2);
if (currentTime < 1) return c / 2 * currentTime * currentTime + b;
currentTime -= 1;
return -c / 2 * (currentTime * (currentTime - 2) - 1) + b;
};
const isInt = n => Number(n) === n;
function getElementOffsetTop(value) {
if (!isInt(value)) {
const elem = document.querySelector(value);
if (elem) return elem.offsetTop;
}
return value || 0;
}
function anchor(element, offset = 0) {
const target = getElementOffsetTop(element);
if (!isInt(element)) {
document.location.hash = element;
}
window.scrollTo(0, target - offset);
}
function animate(element, speed = 500, offset = 0) {
const start = safeScrollTop();
const target = getElementOffsetTop(element);
const change = target - start - offset;
const increment = 20;
let currentTime = 0;
(function animateScroll() {
currentTime += increment;
const val = easeInOutQuad(currentTime, start, change, speed);
window.scroll(0, val);
if (currentTime < speed) setTimeout(animateScroll, increment);
})();
}
function scrollTo() {
return {
anchor,
animate
};
}
export default scrollTo();